LPG is commonly seen as a mixture predominantly i.e. at least 98 vol % consisting of propane and butane, which can be recovered from well-known refinery processes such as hydrocracking. LPG is a valuable gas that is used in industrial and domestic applications and whose demand is steadily increasing in particularly Asia.
Conventionally, LPG is recovered in the fractionation section of a hydrocracking unit by passing a stripper overhead product stream through a sponge absorber (LPG absorber), debutanizer column, deethanizer column, amine absorber and water wash, resulting in an LPG recovery of 90-95% and a LPG product with a hydrogen sulphide (H2S) content of about 35 wppm or less.
Stricter environmental regulations require however lower content of hydrogen sulphide (H2S) in the LPG product, which implies higher capacity of amine absorbers for removing of H2S in the LPG rich streams, or even amine absorbers treating the entire feed gas.
US2015/0053590 A1 discloses a process for improved efficiency of sponge absorption by introducing two different feed points to the sponge absorber, each coming from two separate strippers, i.e. a cold and hot stripper. Accordingly, two strippers are required compared to normally one stripper. Hydrogen sulphide is removed by either treating the entire feed gas in separate amine absorbers or by treating the LPG product stream in an amine absorber.
It would be desirable to reduce the amount of equipment required in the recovery of LPG and to reduce the energy consumption as much as possible, while still maintaining high LPG recovery and required LPG product specifications, not least in terms of H2S content.
It is therefore an object of the present invention to provide a process and plant with LPG recovery of at least 90-95% and with a hydrogen sulphide (H2S) content in the LPG product of not more than 10 wppm, for instance 9 or 5 wppm or even lower.
It is another object of the present invention to provide a process and plant with reduced plot area than prior art processes while still keeping a LPG recovery of at least 90-95% and no more than 10 wppm H2S in the LPG product.
It is still another object of the present invention to provide a process and plant for LPG recovery which is simpler and more flexible than prior art processes, and thereby less expensive.
These and other objects are solved by the present invention.